Three developmental problems are being investigated: The major objective of study of the in vitro development of tooth rudiments in an understading of the factors bearing upon the differentiation of the component tissues. Such studies involve testing the potential for differentiation of isolated tissues and testing the effects of exogenous materials upon the development of of the intact tooth. Studies on the development of the secondary palate of mammalian embryos also focus upon the interrelationships between the component tissues and the capabilities for differentiation of the isolated tissues. The major objective of study of the developing trigeminal ganglion is a definitive description of the cytological specialization of the cells throughout the period of embryogeneis.